Electric home appliances such as water heaters and washing machines are usually provided with an operation input apparatus to operate and control the appliance in an intended way. A press-type input apparatus is a typical operation input apparatus that has a structure as shown in FIG. 5.
The press-type input apparatus 1 includes a tablet sheet 5 which is formed by laminating a pair of resistor plates 2 and 3. The resistor plates 2 and 3 are separated by a slight gap and have uniform resistance layers 2a and 3a formed on the respective surfaces that face each other. This gap between the resistor plates 2 and 3 is created by dot spacers 4 or the like. The tablet sheet 5 is covered partially by a protection cover 6 made of plastic or the like, and the remaining surface of the tablet sheet 5 is exposed.
The front surface side resistance plate 2 contacts the rear surface side resistance plate 3 when a finger or the like presses a selected position on the front surface side resistance plate 2 of the tablet sheet 5. The location of the touch can be obtained after determining the electric potential of the contact point between the front surface side resistance plate 2 and the rear surface side resistance plate 3. The intended input operation is determined based on the information associated with the contact point.
The press-type input apparatus requires applying a significant amount of pressure on the tablet sheet 5. This produces wear on the front surface side resistance plate 2 which eventually becomes deformed after repeatedly pressing the tablet sheet 5. Additionally, since a finger or the like presses on the surface of the front surface side resistance plate 2, the input operation surface tends to become dirty, thereby spoiling its appearance.
For an appliance that exposes the press-type input apparatus to moisture and humidity such as a water heater or a washing machine, it is necessary to create a water-tight seal between the peripheral edge of the exposure window 6a provided on the protection cover 6 and the peripheral edge of the tablet sheet 5. However, when the peripheral edge of the exposure window 6a of the protection cover 6 overlaps a movable part of the tablet sheet, such as a part that moves when pressed, a load is imposed on the overlapped part, potentially causing the apparatus to malfunction. A sufficient boundary must be set for applying pressure, and therefore, there is a limit to reducing the size of the apparatus.
Furthermore, due to the structure of the tablet sheet 5, the surface of the exposure window 6a in the press-type input apparatus is not entirely flat. There is a step corresponding to the thickness of the inner edge of the exposure window 6a. 